Electric safety-catch



(No Model.)

J. W. HOWELL. ELECTRIC SAFETY CATCH No. 460,140. Patented Sept. 29,1891.

I WWI/wow .Xonniia UNITED STATES PATENT OFFICE.

JOHN \V. HOW ELL, OE NEVARK, NEW JERSEY.

ELECTRIC SAFETY-CATCH.

SPECIFICATION forming part of Letters Patent No. 460,140, datedSeptember 29, 1891.

Application filed January 6, 1891. Serial No. 376,831. (No model.)

To aZZ whom it may concern:

Be it known that-I, JOHN V. HOWELL, a citizen of the United States,residing at Newark, in the county of Essex and State of New Jersey, haveinvented a certain new and useful Improvement in ElectricSafety-Catches, of which the following is a specification.

The object I have in view is to produce a practical and effective formof safety-catch for the protection of electrical instruments which arewound with fine wire, such as comparative indicators, telephones,telegraphs, electric clocks, (to. These instruments are liable to beburned out when their circuits become crossed with a circuit, whichcauses an abnormal flow of current through them. A difficulty hasheretofore been experienced in the protection of theseinstruments bysafety-catches, since with metal wire of sizes which can be practicallymade and handled the instruments will be destroyed or injured before thesafety-catch wire is fused, due to the fact that the heat is conservedin the closelycompacted coils of the instruments. By my invention Iemploy for a safety-catch a material which is a conductor of electricityand has a high specific resistance compared with the metals, and whichmaterial is destroyed by chemical action (as distinguished from fusion)when an abnormally large current passes through it. The material may beone which when abnormally heated will combine with the oxygen of the airwith which it is surrounded or will combine with a particular gas withwhich the chamber containing the safety-catch is filled, or the materialmay be one which contains in itself elements which will combine andeffect its destruction upon a rise in temperature. I prefer to employ acarbon for the purpose, the carbon being used in the form of a filamentor wire. An abnormal current heats the carbon safetycatch, and it isoxidized by the surrounding air. Many other materials or compositionscan be used having the characteristics before pointed out. Forillustration, a wire or filament of an explosive mixture, such asgunpowder, can be employed. I11 fact, many materials and compositionswhich are high-resistance conductors of electricity and which can bedestroyed by chemical action when heated abnormally by the electriccurrent can be used, theimportant feature being that the cut-outconductor, containing carbon or other high-resistance material, isheated and destroyed chemically, as described, to interrupt the circuit,rather than being destroyed by a mere fusion of the cutout conductor orby a fusion of wax orother binding agent in which carbon or otherconducting powder is incorporated. A safetycatch made of material ofthis character, by reason of the high specific resistance of thematerial, can be constructed of a large size, compared with a metalsafety-catch which would respond to the same current. I have found thatthese safety-catches can easily be made to open the circuit when acurrent of onetenth of an ampere, or even less,is flowing, and still beof an entirely practical size for handling. The wire, of carbon or othermaterial, may be held between clamps which clamp its ends directly, orany of the wellknoWn methods for making good contacts with carbon may beemployed, such as electroplating the ends of the safety-catch wire wherethey enter the clamps or by securing short lengths of metallic wire tothe ends of the safetycatch wire by any of the methods known in theconstruction of incandescent electric lamps for securing carbonfilaments to leading-wires, the metal and pieces being received bysockets or clamps of any suitable construction. lVhen carbon is employedfor the safety-catch, it should be located in the air, so as to beoxidized when raised to a red heat by the current. It may be inclosed inany suitable safetycatch box which will have or admit sufficient air tooxidize the carbon wire. The carbon wire may be produced in any of theways well known in the manufacture of carbon filaments for incandescentlamps. A great advantage in using a carbon wire for the safety-catch isthat the carbon becomes rapidlythinner and increases its resistanceuntil finally broken. This has the same effect as rapidly inserting aresist ance into the circuit, the final rupture of the circuit takingplace with a much smaller cur rent than it would with a metallic-wiresafetycatch and the tendency to form an are being greatly reduced.

In the accompanying drawing, forming a part hereof, the figurerepresents a side elevation of one form of safety-catch andclamping-holders, a supporting-base and inclosinging-cover being shownin dotted lines.

A B are two spring-clamps, to which are connected the wires 1 and 2 ofthe circuit to be protected. The safety-catch 0, held by the clamps A B,is a wire or filament of car- 'bon, gunpowder, or other material whichis infusible or practically infusible, and is destroyed by chemicalaction when an abnormally large current passes through it. The materialof the safety-catch is one which has, as before explained, a highspecific resistance compared with the metals. The clamps may be mountedupon a suitable base and the whole inclosed by a suit-able cover, asshown in dotted lines. The clamps, or other equivalent mode of fasteningpermits the safety'catch to be readily replaced when burned out.

hat I claim is- 1. A safety-catch for electric circuits, composed of aconductorof electricity which is destroyed by chemical action (asdistinguished from fusion) when an abnormally large current passesthrough it, substantially as set forth.

2. A safety-catch for electric circuits, composed of a conductor ofelectricity having a high specific resistance compared with the metals,and which is destroyed by chemical action (as distinguished from fusion)when an abnormally large current passes through it, substantially as setforth.

3. A safety-catch for electric circuits, composed of carbon,substantially as set forth.

This specification signed and witnessed this 2&th day of December, 1890.

JOHN V. HOWELL.

lVitnesses:

WILSON S. HOWELL, HALSEY M. BARRETT.

